Presentation is loading. Please wait.

Presentation is loading. Please wait.

ODOT BRIDGE LOAD RATING

Similar presentations


Presentation on theme: "ODOT BRIDGE LOAD RATING"— Presentation transcript:

1 ODOT BRIDGE LOAD RATING
Greeting I would like to discuss the next part of this course which will cover ODOT Bridge Load Rating. In the next ½ hour, I would like to discuss. -What a load rating is -Why we perform bridge load ratings -What ODOT expects in a bridge load rating submittal A basic how and why overview

2 What is a Bridge? Federal Highway Administration (FHWA) Definition:
A Bridge is ANY structure that… 1.) is erected over a depression or obstruction (water, highway, railway, etc.) AND 2.) has a track or passageway for carrying traffic or moving loads 3.) has an opening greater than 20’-0” (measured along centerline of roadway between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening) What is a Bridge? Let’s start with the first term of the phrase “Bridge Load Rating”… ON THE SIDE FHWA definition based on the National Bridge Inspection Standards published in the Code of Federal Regulations (23 CFR 650.3) FHWA: "The National Bridge Inspection Standards published in the Code of Federal Regulations (23 CFR 650.3) give the following definition: A structure including supports erected over a depression or an obstruction, such as water, highway, or railway, and having a track or passageway for carrying traffic or other moving loads, and having an opening measured along the center of the roadway of more than 20 feet* between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes; it may also include multiple pipes, where the clear distance between openings is less than half of the smaller contiguous opening. * (6.1 meters)"

3 What is a Bridge? (cont.) Ohio Department of Transportation (ODOT) Definition (based on the Ohio Revised Code): A Bridge is ANY structure that… 1.) is on, above, or below a highway AND 2.) Is greater than or equal to 10’-0” (measured the same way as in the FHWA definition) A 9’ diameter round pipe culvert on a skew could be considered by ODOT to be a bridge) It should be noted that these definitions include: Railroad Pedestrian, and Bikeway bridges. The differences between these definitions is important when it comes to things like… inventory inspection & load rating… …ODOT self imposes a greater range of structures than is actually required of them. ON THE SIDE: ORC: "a bridge is defined as: any structure, including supports, of 10 feet  or more clear span or 10 feet or more (clear opening) in diameter on, above, or below a highway."

4 The “Load” aspect of “Bridge Load Rating”

5 There are Two Primary Types of Loads used in Load Ratings?
Permanent or Dead Loads Structure self weight Superimposed dead loads (barriers, overlays, utilities, etc.) Transient or Live Loads Vehicular loads Impact loads Next let’s look at the “Load” aspect of “Bridge Load Rating”

6 Three Types of Live Loads in Ohio
Design or inventory loads HS20-44, HS25, HL-93 Ohio Legal Loads 2F1, 3F1, 4F1, 5C1 Permit Loads & Superloads Design or inventory loads = Truck configurations developed by design codes such as AASHTO Ohio Legal Loads = Truck configurations developed by ODOT that are used exclusively for load rating. The feds impose live load limitations based on a formula they call the “Federal Bridge Gross Weight Formula”. These Ohio Legal Loads are intended to cover the limits of this formula. And finally… Permit and Superloads are the extra heavy loads that require special permission to travel Ohio highways. IT SHOULD BE NOTED that the feds only require us to use highway loads for load ratings. Consequently, even though pedestrian and railroad structures fall under the definition of “Bridge”, and they are inspected and inventoried, they are not load rated. Note: The Feds only require highway loads to be used for load rating. Consequently, even though pedestrian and railroad structures fall under the definition of “Bridge”, and they are inspected and inventoried, they are not load rated

7 AASHTO HS 25 Truck (current Ohio design load) HS 25 40k 40k 10k
Varies (14’-30’) 14’

8 AASHTO HS 20-44 Truck (still to be used for Ohio load ratings)
Varies (14’-30’) 14’

9 Ohio Legal Loads (2F1) 2F1 2F1 10k 20k 10’

10 Ohio Legal Loads (3F1) 3F1 12k 17k 17k 10’ 4’

11 Ohio Legal Loads (4F1) 4F1 12k 14k 14k 14k 10’ 4’ 4’

12 Ohio Legal Loads (5C1) 5C1 12k 17k 17k 17k 17k 12’ 4’ 31’ 4’

13 What Is Bridge Load Rating?
The safe live load carrying capacity of a highway structure is called its load rating. It is usually expressed as a (rating) factor (RF) of a defined vehicle OR as a gross tonnage for a defined vehicle axle configuration So, after all the dead loads are in place, we are basically asking “How much Live Load can this structure safely take?”

14 Basic Equation for Calculating the Rating Factor (RF)
A load rating can be expressed in terms of a “rating factor” for a particular vehicle. How to calculate the rating factor (RF) A1 = Factor for dead loads A2 = Factor for live load C = Capacity of the bridge D = Dead load effect I = Impact factor L = Live load effect C – A1 * D The factors A1 and A2 depend on which Method and Type of Load rating you are doing. RF = A2 * L*(1 + I)

15 Three Different Load Rating Methods
Allowable Stress (ASD) Also known as Working Stress (WSD) Used for ODOT steel trusses and timber structures Load Factor (LFD) ODOT Preferred FHWA Preferred Load & Resistance Factor Rating (LRFR) NCHRP Project 12-46 Currently, 95% of all ODOT bridges have been load rated using the LFD method. Although the feds are requiring LRFD for design in 2007, ODOT is still planning to require that all load ratings be done using the load factor method. I am told that the feds are still going to REQUIRE Load Factor load ratings for the next 4-6 years.

16 Two Types of Ohio Load Ratings
Inventory Rating (Design Level) 1.) HS20-44 Operating Rating (Service Level) 2.) HS20-44 3.) 2F1 4.) 3F1 5.) 4F1 6.) 5C1 There are TWO types of load ratings Inventory & Operating Ratings The A1 and A2 factors used for Inventory ratings are based on a design level The A1 and A2 factors used for Operating ratings are more based more on an in service condition. Every bridge in Ohio has six different load rating factors calculated.

17 Factors for LFD Load Rating
Ref: AASHTO Manual for Condition Evaluation of Bridges 2000

18 What components of a bridge is ODOT interested in Load Rating
All primary superstructure components of a bridge shall be load rated. Unless specified in a scope, this excludes the following: Decks (unless bridge is a deck slab type) Bearings Substructures Field splices Railing / Parapets

19 When Should a Load Rating be Revised?
The load rating of a bridge should be revised when: there is a change in the dead load on the structure there is a physical change in any structural member of the bridge. there is a change in the proposed live loading A different method of analysis is required Examples of #1 addition or removal of wearing surfaces Sidewalks Parapets Railings Utilities Examples of #2 when there is an alteration in the structure when a new beam or a girder is placed when a new deck is added when there is rusting or damage to a beam, girder or other structural element that has resulted in section loss when there is structural damage to the bridge members due to accidents (i.e. a vehicular collision) when excessive deflection or elongation is observed under temperature or highway loads when there is excessive structural damage (i.e. spalling or salt related damage to concrete) Examples of #3: Permit loads Superloads Example of #4: When codes change (i.e. ASD to LFD and then eventually to LRFR)

20 Why do we rate structures?

21 Why do we rate structures? (1)
The Silver Bridge Collapse The Dec. 15, 1967, collapse of the Silver Bridge at Point Pleasant, Ohio killed 46 people. The failure of the 39 year old eye bar suspension bridge across the Ohio River prompted US Congress to pass National Bridge Inspection Standards (NBIS) in 1968. This collapse prompted the feds to require ORGANIZED inspection departments. It was at this time that ODOT established their Inspection and Load Rating Departments Since the collapse occurred in Ohio, the state felt obligated to stay ahead of these newly established fed requirements… 1.) while the feds required inspections every 2 years, ODOT established annual inspection requirements 2.) while the feds defined a bridge starting at 20’ in length, ODOT defined bridges starting at 10’

22 Why do we rate structures? (2)
Required by Federal government (NBIS) To monitor safety of structures over time To help determine when rehabilitation or replacement is needed

23 Why do we rate structures? (3)
To determine if a bridge needs to be posted for a load restriction as required by the Ohio Revised Code To have a consistent summary of load carrying capacities of all state bridges To assist Office of Permits in their processing of Permit and Superloads Tab #1: Actually, the OHIO Revised Code (ORC), Section doesn’t specifically require load rating. It requires us to post warning signs when a structures capacity drops below a specified threshold. But it is the load rating analysis gives us the needed information to comply with the posting requirement. Tab #2: Different design vehicles have been used in the past for the design of bridges ( e.g., H-15, HS20,  HS25, etc.). Some bridges have aged,  deteriorated or become structurally deficient during the course of their life. To have a consistent summary of the load carrying capacities of all the bridges in the state of Ohio, all bridges are rated using a standard set of vehicles, called Ohio Legal Loads. Tab #3: ODOT has an internal need to load rate structures for the purpose of assisting the Office of Permits in their processing of Superload (vehicles > 120 kips) permits. The Office of Structural Engineering will check all structures along the desired Superload route against the proposed vehicle loading configuration. They will utilize batch routines to re-run already generated models where possible.

24 What is a Permit or Superload Vehicle?

25 A Permit* load equals… any vehicle or combination of loads having a gross weight in excess of 40 tons (or 80 kips). The 40 tons limit was established, because it is the maximum gross weight of the four Ohio Legal Loads (5C1 truck). * = Permits are also required for over-SIZED vehicles. But, for the purposes of load rating, we are referring to permits that are required due to over-weight only.

26 A Superload equals… any vehicle or combination of loads having a gross weight in excess of 60 tons (or 120 kips). The top picture is from Diamond Heavy Hauling company. The transporter is about 205' long and weighs about 200,000 pounds. It is manufactured in Shandon, Ohio. The bottom picture was from a gas turbine transport in The gross weight is 673 kips.

27 Vehicle Categories based on weight
1.50 * 40 NO PERMIT REQUIRED (<= 40 tons) You and me driving our cars on the bridge PERMIT LOAD VEHICLES (40 tons <weight <= 60 tons) - 60 ton limit is based on 150% times 40 tons (the gross weight of the heaviest Ohio Legal Load, 5C1) SUPERLOAD VEHICLES Gross weight of heaviest Ohio Legal Load (5C1)

28 How many vehicle permits are issued each year?

29 Of those permits issued, how many are for Superload vehicles?

30 How many Superload routes does the OSE check each year?
You can see from this chart that the trucks traveling our highways are getting heavier and heavier. This clearly illustrates the importance of knowing the live load limits of each bridge on the inventory. It is also easy to see that there is a need for tools that allow engineers to quickly load rate structures.

31 Computer programs to assist in load rating ODOT bridges
AASHTO BARS-PC (SHALL be used where possible) (http://www.dot.state.oh.us/srg/download.htm) BRASS (SHALL be used for buried structures) (http://www.dot.state.wy.us/generic/brass/index.html) BARS (REQUIRED WHERE POSSIBLE) Steel beams/girders Prestressed and Reinforced Concrete beams/girders Concrete Decks Steel Trusses BRASS Cast-in-place or precast box or frame type buried structures (2’-0” or more of fill on top)

32 Additional Computer programs to assist in load rating ODOT bridges
DESCUS I (www.opti-mate.com) STAAD III/Pro (www.reiusa.com) GT STRUDL (Finite Element based) (www.gtstrudl.gatech.edu) SAP 90 / SAP 2000 (Finite Element based) (www.csiberkeley.com) DESCUS Curved Steel beams/girders STAAD Fairly comprehensive general analysis program. Can do most anything (steel, concrete, prestressed, post tensioned, trusses, etc.) GT STRUDL and SAP 2000 Finite element analyses.

33 Why is BARS desirable to ODOT?
Can run Batch routines (useful for fast analysis of superload routes) Fast, free, and doesn’t require a lot of resources Tested and used over the last 20+ years Provides output in rating format Supports both Mainframe and PC computers Custom vehicles can be easily defined Useful for reviewing new designs

34 BARS on the Internet The program and instruction manuals can be downloaded for free at… An introductory tutorial can be downloaded at… (An AASHTOWARE Product)

35 ODOT Customization of BARS
Custom.std file at… Ohio adopted custom allowable stresses ODOT BDM Tables 904 & 905 Ohio legal vehicles

36 BDM Section 900 Structure Load Rating

37 BDM Section 900 (1) BURIED STRUCTURES
ALL bridges (> 10’) with fill > 2’-0” shall be considered “buried” and shall be load rated EXCLUDING… Circular Steel pipes Circular Plastic pipes Circular Concrete pipes Buried Metal Boxes Buried Metal Frames Junction Chambers Manholes Inlets

38 BDM Section 900 (2) BURIED STRUCTURES (cont.)
All buried structures that are a part of new construction, replacement, or rehabilitation projects shall be load rated as follows… CIP Concrete bridges shall be load rated by the designer using BRASS-Culvert. Precast concrete frames, arches, Conspans, and Bebo type structures shall be load rated by the manufacturer. Precast boxes will be load rated by OSE using BRASS-Culvert.

39 BDM Section 900 (3) NON-BURIED STRUCTURES
ALL bridges (> 10’) with fill < 2’-0” (or no fill at all) shall be considered “non-buried” and shall be load rated BARS-PC SHALL BE USED when possible BRASS-Culvert SHALL BE USED for concrete boxes and three-sided culverts OSE MUST be contacted if any other software is going to be used

40 BDM Section 900 (4) MISCELLANEOUS INFORMATION
Only load rate spans or portions of buried structure that will experience live load Load ratings of new or rehabilitation bridge projects shall be based on final design plans and shall show results that meet or exceed the design loading No FWS shall be included in load ratings TAB #2: Even though the load rating uses an HS20 vehicle, the rating in gross tons for a new project should have results of HS25 or greater since HS25 is now being used as the design load.

41 BDM Section 900 (5) WHEN DO YOU SUBMIT YOUR ANALYSIS?
MAJOR OR MINOR PLAN DEVELOPMENT (OR DESIGN BUILD) PROCESS Include load rating report with STAGE 2 submittal ** MINIMAL PLAN DEVELOPMENT Include load rating report with STAGE 3 submittal ** **Revise and resubmit load rating to District Project Manager if design plans change after Stage 2 (or Stage 3) and prior to contract sale

42 BDM Section 900 (7) WHEN DO YOU SUBMIT YOUR ANALYSIS?
VALUE ENGINEERING CHANGE PROPOSAL (VECP) Include load rating analysis with the Final VECP submission to the District Construction Engineer

43 BDM Section 900 (8) WHAT DO YOU PUT IN THE REPORT?
A full project description Printouts of analysis software input/output Explanation of how material properties were determined (for existing structures) All hand calculations A table summarizing the following rating factors for each live load truck… Inventory & Operating ratings for each main bridge member analyzed (Beam 1, Beam 2, Interior, Exterior, etc.) Overall ratings of each structure unit (mainline, ramps, etc.) Overall ratings of entire bridge Full Project Description would include: PID# Bridge # SFN Bridge Description Methods used Assumptions made All ratings shall be expressed in terms of specific truck tonnages and rounded to the nearest single digit decimal point i.e… RF*20 for HS or RF*(gross vehicle weight in tons for Legal loads)

44 BDM Section 900 (9) WHAT DO YOU PUT IN THE REPORT? 36*1.38 = 49.8
Loading Gross Vehicle Weight (Tons) Rating Factor Member Location Inventory HS-20-44 36 1.38 49.8 tons (HS27.7) Girder 2 Midspan Operating 2.31 83 tons (HS46.1) Ohio Legal Loads (%) - 3.08 308% 2F1 15 4.87 73.1 tons 3F1 23 3.41 78.4 tons 4F1 27 3.09 83.5 tons 5C1 40 123.3 tons 20*1.38=27.7 (Mouse click to get circles) You will notice that even though the gross weight of an HS20 truck is 36 tons the HS rating is 20*1.38 or HS27.7 The Inventory rating in this example is 49.8 tons which is equal to the 1.38 rating factor * 36 tons. The 308% summary rating for the Ohio Legal Loads is equal to the smallest rating factor of all four legal loads times 100. Smallest * 100= 308

45 BDM Section 900 (11) WHAT DO YOU SUBMIT TO ODOT?
2 - Printed copies of load rating report (signed and sealed by an Ohio PE) 1 - Electronic copy of load rating report 1 – Electronic copy of input data files BARS - LISTA.LIS, RATE2.LIS, SUMMARY.LIS, and FLEX.LIS files BRASS - Files with the following extensions: DAT, CUS, and XML Electronic copy can be either a CD or an attachment

46 AASHTO Load Rating References
AASHTO (2002), Standard Specifications for Highway Bridges, 17th ed., AASHTO (2000), Manual for Condition Evaluation of Bridges, 2nd Edition. (Section 6) AASHTO (1995), Bridge Analysis and Rating System, BARS-PC, Release 5.5, Mod 3.3, Users Manuals I and II,

47 AASHTO Load Rating References (cont.)
AASHTO (1989), Guide Specifications for Strength Evaluation of Existing Steel and Concrete Bridges AASHTO (1978), Guide Specifications for Fracture Critical Non-Redundant Steel Bridge Members

48 ODOT Bridge Load Rating References
ODOT (2004), Bridge Design Manual – Section 900 ODOT Structural Rating Group’s

49 Questions??

50 Appendix 1 – Rating Equations
Reference: BARS Manual 1

51 STEEL RATING FACTORS (1)

52 RATING FACTORS BASED ON SHEAR CAPACITY (non-composite)
STEEL RATING FACTORS (2) RATING FACTORS BASED ON SHEAR CAPACITY (non-composite)

53 STEEL RATING FACTORS (3)

54 STEEL RATING FACTORS (4)

55 Composite Steel & Conc. Rating Factors (1)

56 Composite Steel & Conc. Rating Factors (2)
OPERATING (composite, based on Moment Capacity) * whichever is smaller

57 Composite Steel & Conc. Rating Factors (3)
RATING FACTORS BASED ON SHEAR CAPACITY INVENTORY

58 Composite Steel & Conc. Rating Factors (4)
RATING FACTORS BASED ON SHEAR CAPACITY OPERATING where Vp = shear yielding strength of the web

59 Composite Steel & Conc. Rating Factors (5)

60 Composite Steel & Conc. Rating Factors (6)

61 Reinforced Concrete Rating Factors (1)

62 Reinforced Concrete Rating Factors (2)

63 Prestressed Concrete Rating Factors (1)

64 Prestressed Concrete Rating Factors (2)

65 Appendix 2 – Load Rating Example

66 Single-span slab bridge
Bridge #: SEN Over: Branch of Wolf Creek SFN: Clear Span: 16’-0” Slab thickness: 11.5” Slab Width: 40.5 ft Overlay: 3” asphalt on ¾” soil Long. Bottom Steel: 4 ½” Transverse Bottom Steel: 5’s Analysis Software: BARS-PC Input filename: R DAT

67

68 Live load distribution factor
AASHTO Standard Specification for Highway Bridges 2002 CASE B – Main Reinforcement Parallel to Traffic S = Effective Span length in feet (AASHTO ) For wheel loads, the distribution width E = *S  7’ S = 16+1 = 17 feet E = *17 = 5.02 feet BARS Dist. = 1/5.02= 0.199

69 Impact load (Impact factor)
AASHTO Standard Specification for Highway Bridges 2002 3.8.2 Impact Formula The amount of impact allowance, I, as a fraction of the live load I = 50 / (L + 125)  0.3 L = Effective Span length in feet I = 50 / ( ) = 0.352 Use I = 0.3

70 Superimposed Dead Load
((3” / 12)* 1 ft* 145 pcf) + ((3/4” /12) * 1 ft * 120 pcf) + 12 plf guardrail = lb/ft Rebar distance to top of slab (11.5”–1” clear due to delamination- 5/8”–(7/8”) / 2 ) = 9.4375”

71 Interactive Bridge Data Entry
AA NEW X DMH - B&N *LF* POST SPEC SPEC 17.0 DMH - B&N BSEN LF SEN OVER BRANCH OF WOLF CREEK, SFN: SINGLE SPAN CONCRETE SLAB BUILT IN 1926, 16 FOOT CLEAR SPAN " ASPHALT W.S. (DATE: N/A) ON 0.75" OF SOIL, 40.5' SLAB WIDTH S RC S W S S

72 Load Rating Summary Loading Gross Vehicle Weight (Tons) Rating Factor
Member Location Inventory HS-20-44 36 0.58 20.90 tons (HS11.61) Conc. Deck Midspan Operating HS-20-44 0.97 34.85 tons (HS19.36) Ohio Legal Loads (%) - 1.07 107% 2F1 15 1.55 23.2 tons 3F1 23 1.19 27.4 tons 4F1 27 29.0 tons 5C1 40 47.7 tons

73 APPENDIX 3 – Where to get more help ?
BARS Manuals Limited support from Structure Rating Section Amjad Waheed, PE Shelton A. Howard, PE Richard C. Irwin, PE Cindy Wang, PE


Download ppt "ODOT BRIDGE LOAD RATING"

Similar presentations


Ads by Google